In the arts of producing electronic components and attaching the components to circuit cards, terminal on the components are normally attached to connectors on circuit cards using joints of solder. The most common method of applying solder is to form holes through the circuit board, plate copper into the holes, position components on top of the board with pin terminals extending through the holes, and dip the bottom of the board in a bath of molten solder.
More recently surface mount components have been developed which are attached to pads on circuit boards by screen printing a paste of solvent and solder particles onto the pads and then placing the terminals of components on the pads and then moving the board through an oven to heat the paste enough to melt the solder and form a solder joint. The solder commonly used in the electronics industry is an alloy of tin and lead which has lead to environmental concerns. In addition the high processing temperature required to melt the solder paste limits the materials that can be used in electronics.
Those skilled in the art are directed to the following citations. U.S. Pat. No. 5,376,403 to Capote, Todd, Manesis, and Craig, and a paper entitled Multilayer Printed Circuits From Revolutionary Transient Liquid Phase Inks by Capote, Todd, Gandhi, Carr, Walters, and Viajar, presented at Nepcon West '93, Feb. 11, 1993, suggest mixing a high melting point (up) powder, a low mp solder powder, a fluxing agent, a resin and a reactive monomer or polymer to form a polymer thick film ink. Also, the high mp powder may be coated with solder to prevent oxidation, and a third powder such as Ni powder thinly coated with Au may be added to provide transient liquid phase (TLP) bonding. Using ORMET.TM. 1200 by Toranaga Technologies, Inc. in Technical Note #9 Rev. 2 Jan. 12, 1994. Using ORMET.TM. 2005 by Toranaga Technologies, Inc. in Technical Note #3 Rev. 6 Jan. 30, 1994. Solders and Soldering by H. H. Manko (McGraw Hill, 1979) lists various solders and their properties. U.S. Pat. No. 5,129,962 to Gutierrez describes no-clean fluxing agents for flip chip attachment. U.S. Pat. No. 5,268,536 to Kakehi suggests attaching leads to pads using conductive adhesive.
Polymers made electroconductive by filling with electroconductive particles is suggested by U.S. Pat. Nos. 5,410,806 to Schneider; 5,395,876 to Frentzel; 5,286,417 to Mahmoud; 5,136,365 to Pennisi; 4,780,371 and 4,859,268 to Joseph. U.S. Pat. No. 5,463,190 to Carson suggests polymers filled with powders of two different elements in eutectic proportions. Transient Liquid Phase bonding is suggested by U.S. Pat. Nos. 5,432,998 to Galasco; 5,346,857 to Scharr; 5,269,453 to Melton; 4,147,669 and 4,233,103 to Shaheen; 3,523,358 to Zimmer; and by the citations Development of Transient Liquid Phase Soldering Process for LSI Die-Bonding by Izuta, Abe, Hirota, Hayashi and Hoshinouchi of Mitsubishi Electric, in 1993 IEEE Proceedings of Elect. Comp, & Tech. conf. P. 1012-1016; Transient Liquid Phase Bonding Process by Kang et al in IBM TDB Vol. 32, No. 4A, September 1989. Semiconductor Joining by the Solid-Liquid-Interdiffusion (SLID) Process by Leonard Bernstein in Journal of the Electrochemical Society Vol. 113, No. 12, pp 1282-1288 December 1966. U.S. Pat. No. 5,242,099 to Ueda suggests making metal bonds between a surface with a thin diffusing layer and another surface with a target layer. Coating of metal particles is suggested in U.S. Pat. No. 4,902,857 to Cranston.
U.S. Pat. No. 5,024,372 to Altman discloses use of photoresists for screening solder paste. U.S. Pat. No. 5,436,503 discloses conductive adhesives for chip connection. European Application EP307766 A1 discusses screening paste into a layer on a circuit board. European Patent Application EP0697727 A2 discloses screening solder paste into a lift off mask. U.S. Pat. No. 5,074,947 to Estes discloses conductive polymer bumps on a flip chip with two layers. U.S. Pat. No. 5,314,709 to Doany discloses an evaporatable dielectric. U.S. Pat. No. 5,001,829 to Schelhorn discloses a removable stencil for solder paste. All the above citations are hereby-incorporated herein by reference.